Draft Indian Standard TEST PROCEDURE FOR THERMOSYPHON TYPE DOMESTIC SOLAR HOT WATER HEATING SYSTEMS ICS ; ;

Transcription

1 Draft for Comments Only Do: MED 04(1050)C Draft Indian Standard ES PROCEDURE FOR HERMOSYPHON YPE DOMESIC SOLAR HO WAER HEAIN SYSEMS ICS ; ; Not to be reprodued without the permission of Last date for reeipt of BIS or used as a SANDARD omments: 31 August 2009 FOREWORD Formal adoption lause to be added later on. he overnment of India has been promoting solar thermal systems and devies in the ountry by implementing wide ranging programmes. As a result, signifiant industrial infra-struture has been established for manufaturing of these systems and devies, and new design variations have also emerged over the period of time. he solar thermal industry is manufaturing different types of solar water heating systems and the government is implementing various programmes related to large-sale promotion and dissemination of this tehnology. his test proedure is envisaged for testing of the domesti solar water heating systems manufatured by the solar thermal industry. he test proedure would enable quality ontrol of the solar water heating systems promoted and disseminated in the ountry. he standard has been formulated to evolve a uniform test proedure for solar hot water systems, espeially of domesti type, using flat plate olletor or evauated tubular olletor. he standard is based on a draft test proedure developed at Indian Institute of ehnology, Bombay under a Researh and Development Projet sponsored by the Ministry of New and Renewable Energy and further experiments onduted at Regional est Centre, Devi Ahilya Vishwavidyalaya, Indore. For the purpose of deiding whether a partiular requirement of this standard is omplied with, the final value, observed or alulated, expressing the result of a test or analysis, shall be rounded off in aordane with IS 2 : 1960 Rules for rounding of numerial values (revised). he number of signifiant plaes retained in the rounded off value should be the same as that of the speified value in this standard. 1 SCOPE his standard applies to evaluate thermal performane of domesti solar hot water systems, using Flat Plate Colletor (FPC) or Evauated ubular Colletor (EC), working on thermosyphoni flow of water under natural outdoor onditions. he solar water heating system may employ eletri heater in the storage tank as an auxiliary soure of heating, however performane of the system is evaluated under solar operation mode only.

2 his standard may also be applied to solar water heating systems employing unglazed/glazed solar flat plate olletor, or any other non-onentrating design of solar olletors with appropriate benhmarking of performane parameters. his standard does not apply to solar hot water systems employing onentrating solar olletors. 2 ES SYSEM 2.1 Requirement for the System Submitted for the est A omplete set of domesti solar water heating system, designed to work on thermosymphoni flow, shall be ereted at the test site by the manufaturer / supplier in onsultation with the testing laboratory. he system shall onsist of a solar olletor, a storage tank of appropriate apaity and piping to onnet inlet and outlet of the solar olletor to the storage tank. he piping may be insulated in aordane with the speifiations of the systems marketed by the manufaturer. he testing shall be arried out on the system on as-installed basis. Any deviation in the speifiations may render test report invalid. 2.2 Speifi Requirement of ank for the est he tank of the system submitted with the system for testing should have inlet/outlet of 1 size and on 1 pipe opening at the top entre of the horizontal ylindrial tank for inserting RD Sensor 3 NOMENCLAURE A ross area of solar olletor, m 2 A a Absorber area of solar olletor, m 2 A p otal outside surfae area of the onneting pipes, m 2 A p otal outside surfae area of pipes whih may be effetive for loosing heat during night-test, m 2 A s Outside surfae area of storage tank, m 2 C p Speifi heat of water, J/kg K F Colletor effiieny fator Solar irradiane on the inlined plane of the solar olletor, W/m 2 Average value of solar irradiane on the inlined plane of the solar olletor during day-test, W/m 2 (MC) s hermal apaitane of the water in the storage tank only, J/K Q otal energy olleted by the solar olletor during period of the day-test, kwh Q otal solar radiatiant energy inident on the olletor during day-test period, kwh t ime, s a Ambient air temperature, ºC ad Average ambient air temperature during day-test, ºC an Average ambient air temperature during night-test, ºC m Cold water temperature from mains, ºC s emperature of water in storage tank, o C sfn Final Storage tank water temperature at the end of night-test, ºC 2

3 sfd Final Storage tank water temperature at the end of the day-test, ºC sid Initial Storage tank water temperature at the start of the day-test, ºC sin Initial Storage tank water temperature at the start of the night-test, ºC sn,m Storage tank water temperature at m th interval during the night time, ºC U sys, d Average Overall heat loss oeffiient of the system during day-test, W/m 2 K U L Overall heat loss oeffiient of solar olletor, W/m 2 K U sys, n Average Overall heat loss oeffiient of system during night-test, W/m 2 K U p Overall heat loss oeffiient of piping, W/m 2 K Overall heat loss oeffiient of storage tank, W/m 2 K U s reek Symbol t ime duration of solar test, s η Maximum effiieny of the system averaged over the day- test period sys,o η sys Effiieny of solar hot water system averaged over the day- test period (τα) eff Effetive transmittane absorptane produt of the solar olletor for solar radiation τ ooling Cooling time onstant during night time test-period Subripts a d f i m n p s ambient Conditions olletor day time final value Initial Value mains, m th time night time pipe storage ank on tilted olletor surfae 4 MEASUREMENS 4.1 Physial Parameters All physial measurements, suh as, length, width, thikness, et. shall be measured and reported in mm. ross area of solar olletor is defined as the total area on whih solar radiation is falling (taking into aount the gap, if any, between the tubes, and also the frame et. of the EC based system and of the olletor box of the FPC based system).it shall be alulated by multiplying width and length of the olletor measured from outer edge to the outer edge. For the solar water heating models using all-glass ECs, length shall be measured from bottom side of the storage tank to the outer edge of bottom tube holder while width shall be taken as equal to the length of the bottom tube holder. he measurement auray of the gross area shall be ± 0.1 %. he volume of the storage tank shall be measured to an auray of ± 1%. 3

4 4.2 Climati Parameter Solar radiation shall be measured using a lass-i Pyranometer on the plane parallel to the solar olletor. For this, a separate mounting stand shall be used For measuring ambient air temperature, the measuring sensor (a alibrated RD) shall be loated shaded by a Stevenson sreen in the viinity of the test set-up (not more than 10 m from it. It shall be ensured that there is no obstrution by any struture or building to alter (blok or enhane) the free flow of the natural wind to the sensor. he outside surfae of the Stevenson sreen shall be of light olour, preferably white, and its bottom shall be kept at least 1 m above the ground level he surrounding air speed shall be measured on the olletor surfae every half an hour with an auray of ± 0.1 m/s and the average value of the day will be reported along with the test results. 4.3 Performane Parameter he duly alibrated RDs shall be used for measurement of water temperature. he auray of measurement shall be ± 0.1ºC or better. Measurements shall be made at three loations in the storage water tank. For this, measuring sensors shall be inserted through the opening provided by the manufaturer at the top entre of the tank. he sensors are plaed at equal vertial distane from eah one and from the top and bottom of the inner tank. he storage water tank temperature at any time t sm will be taken as mean of the temperature measured by the three RD s he pressure shall be measured to an auray of 5% of atual reading Elapsed time measurement shall be made to an auray of ± 0.2%. Computer based systems shall be used for data monitoring and logging. Analog or digital reorders shall have auray equal to or better than ± 0.5 % of the full-sale reading and have a time onstant of 1 s or less. he peak signal indiation shall be between 50 % and 100% of full sale. 5 SEQUENCE OF ES 5.1 he est shall be arried out in the following sequene Sequene est 1 Pre-onditioning est 2 Stati pressure Leakage est 3 hermal Performane est (Day-time and Night-time tests shall be performed one after another to omplete one data set) 4

5 6 ES PROCEDURES 6.1 Pre-Conditioning est Fully assembled system filled with water shall be kept exposed to weather onditions for 15 days having daily solar irradiane on the plane of solar olletors more than 16 MJ/m 2. he days with solar irradiane lesser than this value shall not be ounted All parts of the system shall be inspeted for any visual sign of degradation, deformation, ingress of moisture/dust, et. and shall be reported. 6.2 Stati Pressure Leakage est he purpose of this test is to ensure the integrity of Solar Hot Water System partiularly its tank to withstand the pressure, whih it might meet in servie. Shemati of test set-up for onduting this test is shown in Annexure I Initially, air bleed valve is kept open and it is ensured that all air is removed from the olletor by irulating water though it. hereafter, the solar Water Heating System (tank + olletor) is filled with water at a temperature of 60 ± 2ºC. After filling, the bleed valve and all other valves are losed, and a hydrauli pressure 5.0 kg/m 2 is applied for flat plate olletor system and a hydrauli pressure of 0.2 kg/m 2 is applied for evauated tabular olletor system. he system is kept pressurized for a period of 30 min for EC system After 30 minutes, all parts of the system, espeially the storage tank, shall be inspeted for visual sign of any leakages. Results of the test in terms of the initial and final reading of the pressure gauge, temperature of the water, duration of the test and the result of inspetion shall be reported. 7 HERMAL PERFOMANCE ES 7.1 he test method is based on a lumped apaitane model, where it is assumed that average water temperature in the storage tank haraterizes the behaviour of the whole system whether the storage is well mixed or stratified. 7.2 he test proedure envisages haraterizing the thermal performane of the system without any withdrawal of hot water from the storage tank. his strategy is adopted beause the performane of the solar water heating system strongly depends on the pattern of withdrawal of hot water from the storage tank, and there ould be wide variation in the withdrawal pattern. 7.3 he system performane is evaluated in two parts orresponding to its performane during daytime and separately during nighttime. Usually, the storage tank in solar water heating systems whih are designed to work on the priniple of thermosyphoni flow is loated at higher level than the top edge of the solar olletor with a view to suppress reverse flow during night. In suh a ase, the solar olletor and part of piping would not play role in loosing heat from the tank during night as it does during the day. However, nighttime test would aount for all thermal losses from the system. 5

6 7.4 Day-ime Performane he following energy balane equation would determine the thermal performane of the solar hot water system during the day-time: Rate of hange in Rate at whih useful Rate at whih energy energy ontents of = energy is sup plied to is lost from water the water in the water in the storage tan k in the storage tan k storage tan k by solar olletor to the ambient air (1) Mathematially, this may be expressed as follows: (MC) s d s = A a F [ (τα) eff U L ( s - a )] - (A s U s + A p U p ) ( s - a ) (2) dt Rearranging and integrating equation (2) with respet to time, between the time period t 1d to t 2d during whih the energy is olleted, one gets (MC) s ( sfd sid ) = A a F t 2 d (ατ) eff.dt - (A a F U L +A s U s +A p U p ) ( s a ) dt (3) he total energy inident on the olletor during the time period from t 1 to t 2 is given by the following expression: Q S = A t2d dt (4) Dividing equation (3) by equation (2), one gets t2 d η sys = sys, o η U sys, d. X (5) where η sys = ( MC) A ( s sfd t2d dt sid ) (6a) η sys, o = A a F' A t 2 d t1 d t d2 ( ατ ).dt eff.dt (6b) U sys, d = A F' U + A U + A a L A s s p U p (6) 6

7 X = t 2d ( s t 2d ) dt a dt Do: MED 04(1050)C he parameters η sys, o and U sys, d are defined as the harateristi parameters of the thermosyphoni solar water heating systems during the day-test period. 7.5 Night-ime Performane During night time, no solar radiation is reeived and also there is no flow of water through the solar olletor. he heat is therefore lost primarily from the storage tank and part of the piping. In view of this, the equation (3) may be re-written as follows: (6d) or t n ds MC s 2 ( ) = - (A s U s + A p U p ) dt (7) t n s 1 a sfn an ( MC) s ln = U sys, n.a (t 2n - t 1n ) (8) sin an Where U sys, n.a = (A s U s + A p U p ) and t 2n - t 1n =10 hrs=10 x 3600 se. (8a) Cooling time onstant to rate the performane of the solar water heating system during no-radiation period may be expressed by the following expression: ( MC) s τ ooling = = ( U sys, n. A) [t 2n 1 - t 1n ] sfn an ln (9) sin an Here, the τ ooling represents the time at whih the differene between the hot water temperature in the tank and the mean ambient temperature drops to 36.8% of its initial value. 8 ES CONDIION 8.1 he total duration required for one yle of the daytime test is 7h, omprising 3.5h before solar noon and 3.5 h after solar noon. he total solar irradiane during the test duration of 7h shall be greater than or equal to 14 MJ/m 2. he ratio of solar irradiane in the forenoon and afternoon periods, eah of 3.5h, shall lie in between 0.5 and 1.5. he average value of wind speed during the test period shall be less than 4 m/s. 9 EXPERIMENAL DEERMINAION 9.1 hermal performane of the thermo-syphon domesti solar hot water system shall be haraterized by three parameters viz. η, U sys, d and τ ooling under this test proedure. he sys 7

8 8 Do: MED 04(1050)C testing of the system shall be arried out in two steps, namely, the solar test (day-test) and the no-solar test (night-test). As the present test proedure proposes tests under onditions of noload withdrawal, the performane thus obtained may be treated as the lower limit of the performane. 9.2 A shemati sketh of test-up is given in Annexure-I. he main omponents of the test set up are as follows. (i) Domesti solar water heating system, as installed by the manufaturer, onsisting of solar olletor(s), storage tank, inter-onneting piping, and supporting stand. (ii) A hydrauli loop integrated with the test set-up, onsisting of a irulating pump (apaity > 40 lpm) for mixing the water, one Rota meter to measure water irulation rate, a hydrauli pressure soure, bleed valve, pressure gauge, and other aessories. (iii) Measurement system, whih shall inlude a omputer based data logging systems, instruments / sensors for measuring solar radiation on the plane of solar olletor, ambient air temperature in the viinity of test set-up, air veloity on the plane of solar olletor, and pressure gauge, along with neessary fixtures for their installation. 9.3 It shall be ensured that there is no shadow or obstrution to the solar radiation falling on to the solar olletor or onto the Pyranometer during the period of day test. Also, all the piping inluding for hot water withdrawal, mixing pumps et. shall be insulated with 50 mm glass wool insulation with neessary ladding to protet it from moisture ingress et. Provision of old water supply shall also be made. 9.4 Day-ime est Shall Be Conduted In he Following Steps: (i) Determine Indian Standard ime (IS) orresponding to the solar noon (ii) Solar olletor is shaded ompletely with an opaque over, white on the top exterior, at about 4 h before the solar noon. he storage tank of the solar water heating system is filled fully with water. he quantity of water filled in the storage tank shall be taken as notional apaity of the solar water heating system. (iii) he water in the storage tank is fully mixed by swithing on pump for 5 minutes before beginning of the test at the designated time instant. (iv) Initial value of the storage water temperature, sid is measured and reorded, and the shade-over is removed at 3 h 30 min before the solar noon. (v) Measurements for ambient air temperature, water temperature of the storage tank, and solar irradiane on the plane of solar olletor get ommened at the start of the test. he measurements are ontinued subsequently for the entire period of the test at an interval of one minute or less, however, reording of data is adequate at an interval of 10 minutes. (vi) o end the day-test yle, the solar olletor is again shaded on expiry of 3 h 30 min from solar noontime. he water in the storage tank is again mixed by operating the pump for five minutes, and final storage water temperature ( sfd ) is measured and reorded. (vii) he test is repeated for at least ten days with different values of initial storage water temperature. he first test shall be arried out with old (supply) water in the storage tank. For subsequent days, initial water temperature shall be raised in uniform steps to over up to 70ºC temperature (fully mixed storage).

9 (viii) (ix) Different initial temperature in the storage tank may be ahieved by adding appropriate quantity of old water to the previous day s heated water in the storage tank. Alternatively, hot water from any other soure may also be used to ahieve the required temperature of the water in the storage tank. he data may be reorded in a format given at Annexure II. 9.5 Night-ime est: Night-time test essentially intends to find out overnight heat loss harateristis of the solar system. he duration of test is 10 h under no-solar onditions. he following steps are undertaken to perform this test: (i) (ii) (iii) (iv) (v) (vi) Measure the amount of solar radiation falling on the plane of solar olletor (s) before starting the night-test; if the measured value is more than 50 W/m 2, over the solar olletor (s) by an opaque shield. his may be done by fixing the over leaving a, gap of about 0.5 m above the solar olletor(s) to allow free flow of surrounding air. After the solar radiation falls below the value of 50 W/m 2, the over should be removed. Swith on the mixing pump for about 5 minutes before the start of night-test time so that water temperature in the storage tank is fully mixed and attains uniform temperature. Undertake measurement of initial storage water temperature, sin. Carry out measurements of water temperature of storage tank, and ambient air temperature at an interval of ten minutes during the test period. Again, swith on the mixing pump at the end of test period of for about 5 minutes and measure final storage water temperature, sfn. Repeat the experiments for number of days for whih the da-test was performed. he data may be reorded in a format given at Annexure III. 9.6 Computation Based on the measured data obtained during day-test and night-test, the harateristi parameters of the solar hot water system shall be evaluated as given subsequently Calulate η sys from the following expression using data reorded during the daytime test: η sys = (MC) A ( s sfd t 2 t1 dt sid ) he alulation of X involves integration of storage water temperature over the duration of daytime test, as is lear from equation (6d). For this, the test period is broken into m- intervals, eah of 10 minutes, and pieewise integration is performed for eah of the m th time interval using the following expression: X = t2d ( sd t2d ad dt ). dt = 42 m= 1 ( sfm + sim ) adm ( t2m t 2 42 ( fm + im ) ( t2m t1 m ) m= 1 2 d ) 1m d (11) (12) 9

10 where adm represents average ambient temperature during the m th time interval; sfm and sim represents the water temperature of the three RD s in the storage tank at the end and start of the m th time interval, respetively. Similarly fm and im are the solar irradiane value reorded at the end and at the start of the m th time interval obviously, the value of (t 2m t 1m ) d in the above expression is equivalent to 10 minutes Plot a urve with values of η sys on y-axis and those of X on x-axis. Draw a trend line using regression method of least squares of urve fitting, and obtain for all the ten days values of η sys,o and U sys, d from the interept of the trend line with y-axis and slope of the trend line respetively System effiieny orresponding to the following standard test onditions may be alulated using equation (5). Average storage temperature = 50ºC Average ambient air temperature during test period = 25ºC Average of total solar radiation inident on the plane of = 700 W/m 2 solar olletors Amount of thermal energy stored in the storage tank during a period of seven hours orresponding to the standard test onditions in kwh may be alulated as follows: Q = ( orresponding to s tan dard onditions) xa x0.7 x7 (13) η sys he value of τ ooling an be alulated using equation (9). τ ooling an also be alulated by plotting a straight line urve between ln [ sn, m an] versus time t m,n. sn,m is the storage tank water temperature at t m,n time thus obtained. he inverse of the slope of the trend line will give τ ooling. 10 ES REPOR 10.1 A test report shall be generated in the format given at Annexure IV. 10

11 ANNEXURE - I (Clause 6.2.1) Vinson Sreen Air -Vent Pyranometer Evauated ubular Colletor Storage SStorage ank Pressure auge Bleed Valve Hot Water Draw-Off Anemometer Hydrauli Pressure Soure Mixing Pump Rotameter Supporting Cold Water Supply Shemati Diagram of the Experimental Set 11

12 ANNEXURE II (Clause 9.4) Day-time est Format to reord test results ime (hrs) 0000 ad (ºC) (W/m 2 ) Storage water temperature (ºC) Sensor 1 Sensor 2 Sensor Average 3 Wind Speed (m/s)

13 ANNEXURE III (Clause 9.5) Night-time est Format to reord test results ime (hrs) 0000 Ambient emperature (ºC) Sensor 1 Storage water temperature (ºC) Sensor Sensor Average

14 ANNEXURE IV (Clause 10.1) Offiial Stationary of the est Laboratory/ Institution Address and Contat Details ES REPOR A. ENERAL 1. Name and Address of manufaturer/supplier 2. Contat details of manufaturer /supplier 3. Details of sample submitted/model, if any 4. Latitude & Longitude of test laboratory Latitude Longitude 5. Duration of the est B. SPECIFICAIONS OF HE ES SAMPLE (All dimensions are in mm, unless speified otherwise) 1. Evauated ube Colletor (EC) a Make/Model b Complete address of the manufaturer inluding / web site et. ype (All glass diret flow/ Heatpipe type/ Any other (pl. speify) d ube length e Inner diameter of inner tube f Outer diameter of outer tube g Number of tubes h Details of seletive oating (data from manufaturer may be used) i Exposed area (gross) of a single ube (Di L), m² j ross aperture area of the olletor, m² k Refletor below the tubes (Provided/Not Provided) Do: MED 04(1050)C 14

15 2 Flat Plate Colletor a Box material b Box length Box hikness d Box width e Absorber material f Absorber thikness g Absorber oating h Insulation thikness (Bak) i Insulation thikness (Side) j k-value at 100 C,Wm -2 K -1 k BIS Certified ( Yes/No) l BIS Certifiate No Attah a Copy 3. Storage ank a b Inner tank thikness and material Material and thikness of outer ladding Capaity (Kg) (without taking into aount water in the olletor) d e f Material & thikness of insulation i) Plane side of tank ii) Cirular side of tank Height of hot water withdrawal point from bottom of the tank Height of old water inlet point from bottom of the tank 4. Conneting Pipes a Material b Outer/inner diameter Outer surfae oating d Insulation material and thikness 5. Supporting Stands/Frame a Material b ype and hikness Outer surfae oating 15

16 C. ES RESULS 1. Pre-onditioning test Results of inspetion after 15 days of test 2. Stati Pressure Leakage est a Initial & Final Pressure (kg/m 2 ) b emperature of water in the storage tank ( o C) Duration of the test period (min) d Results of inspetion Leakage observed /not observed 3. hermal Performane est a Perentage Maximum effiieny of the system, η sys,o b Overall heat loss oeffiient of the system during day-time test, U sys,d (W/m²K) d e f g Night-time heat loss oeffiient of the system, U sys,n, (W/m²K) and τ ooling,n (days) Perentage System Effiieny at Standard est Conditions ( S =50ºC, ad =25ºC, =700 W/m²) Average amount of energy olleted (Q) during the period of daytime test orresponding to standard test onditions (kwh) A table of the data points for daytime test along with values of wind Attahed speed (averaged over the test period). A graph between X & η sys Attahed 4. Any Other Detail 5. Remarks Date: Plae: (esting Offier) (Head of the est laboratory) 16